1. Field of the Invention
The present invention relates to an improvement in a transfer mold for semiconductor resin sealing.
2. Description of the Related Art
Conventionally, the transfer mold for semiconductor resin sealing has a plurality of rod-like heaters 7, for example, as shown in FIG. 1. In general, the mold temperature is monitored by one or a plurality of sensors 8 and the heater 7 and sensor 8 are controlled by a control section 9.
Since the rod-like heater 7 has a given heat generation distribution, it is necessary to initially select the characteristic of the heater upon manufacture. If, therefore, the heat generation distribution of the heater is varied, the heater by itself has to be replaced by a new one having a characteristic near that distribution.
For the conventional rod-like heater it is necessary to initially select the heater characteristic upon manufacture and the temperature distribution on the surface of the heating plate is determined by the characteristics such as the quantity of heat. Further, even when the characteristic of the heater is so determined as to obtain desired heat generation distribution, this determination is made after repeated trial-and-error actions. This incurs a longer trial period of time and added costs.
As shown, for example, in FIGS. 2 and 3, when a heater 7a (FIG. 2) is selected so as to obtain uniform temperature distribution on the heating plate, the temperature distribution of the heating plate is made uniform. In order to obtain the uniform temperature distribution of the heating plate, it is necessary to replace the heater 7a (FIG. 2) with a heater 7b (FIG. 3).
The temperature distribution of the heating plate can be freely set in one direction by varying the set temperature of respective heaters in a direction in which these heaters are arranged as a pitch array. However, the temperature distribution of the heating plate cannot be freely set in another direction because it is determined by the heat generation characteristic of these heaters in an axial direction of the respective heater, that is, in a direction in which the heater is inserted.
For the semiconductor resin sealing mold arranged on the heating plate with to-be-heated products placed therein, it is difficult to set temperature at any given area on the heating plate due to variation in quantity of heat on the heating plate. In order to compensate for some lack in the quantity of heat by and reach necessary heat generation distribution, an external heater, etc., and an extra space, etc., are necessary.
It is thus necessary to initially select the characteristic of the heater upon manufacture. The temperature distribution is determined by the heat generation characteristic of the heater in the insertion direction of the heater and cannot be freely varied when there occurs a variation in the quantity of heat, etc.